1. Field of the Invention
This invention relates to clamping pins within devices for external fixation of fractured bones, and, more particularly, to an external fixture in which pins are clamped for fixation of a fractured radius.
2. Background Information
The fracture of the distal radius is one of the most common human fractures, occurring in as many as 350,000 people per year in the United States alone. The conventional processes both for reducing such a fracture and for maintaining the bones in proper alignment during the subsequent healing process involves applying and maintaining an extension force across the fracture, with ligamental taxis being relied upon to hold the bones in place. The process for treating a fractured distal radius is described in the 1901 edition of Gray's Anatomy in the following manner, "The treatment consists of flexing the forearm, and making a powerful extension from the wrist and elbow, depressing at the same time the radial side of the hand, and retaining the parts in that position by well-padded pistol-shaped splints."
A common method for the treatment of a fractured distal radius involves the use of standard immobilizing cast techniques, preventing movement of the radiocarpal joint throughout the course of rehabilitation. A problem with this method is that it sometimes results in inadequate internal fixation, which can cause deformity, pain, and prolonged disability.
The process of external pin fixation is often used in the repair of a fractured distal radius. This process initially involves the surgical insertion of skeletal traction pins on both sides of the fracture, with a frame being connected to the pins for immobilizing the bones, and for holding them together until the fracture is mended. Conventional methods for applying external pin fixation for the treatment of a fractured distal radius provide for the immobilization of the radiocarpal joint, so that the hand cannot be flexed. Examples of frames used in this way are found in U.S. Pat. Nos. 4,554,915 and 5,545,162. Each of these frames rigidly but adjustably connects a pair of pins extending into the metacarpal bones with a pair of pins extending into the radius on the proximal side of the fracture. While this type of fixation often provides an improvement over conventional casting techniques in the management of severe fractures of the distal radius, immobilization of the radiocarpal joint during the treatment period typically results in a long period of stiffness and disability after the external fixation device is removed. Typically the external fixation device is left in place during the healing process for six to eight weeks. After the fixation device is removed, three to six months are required for the patient to regain motion of his hand. Thus, what is needed is a fixation device providing adequate fixation during the healing process while allowing flexure in the radiocarpal joint.
A fractured distal radius may alternately be repaired using a permanently installed fixation plate with screws and blades extending into the radius and into the broken-away fragment, as described, for example, in U.S. Pat. No. 5,006,120. What is needed is a method for combining the benefit of this method for installing an internal fixation plate, in terms of early flexure of the hand at the radiocarpal joint, with the benefit of the relatively simple surgical procedures of external pin fixation.
U.S. Pat. No. 4,747,400 describes an external fixation frame including a proximal carriage on one end and a distal carriage on the other end. The proximal carriage is adapted to mount pins inserted into the proximal bone segment, and is supported on the frame by support arms which are movable with respect to the frame. The distal carriage includes a clamping member, adapted to mount pins inserted in the distal bone segment, which is pivotal about the fracture to permit precise alignment of the distal and proximal bone segments. A fragment support, mounted to one of the side rails of the support arm for the proximal carriage, is adapted to clamp a pin inserted within a central fragment positioned between the proximal and distal segments of a comminuted fracture.
The external fixation frame of U.S. Pat. No. 4,747,400 is a general purpose device for dealing with fractures of long bones, such as the femur, tibia, humerus, ulna, and tibia, as well as the radius. Since fractures of the distal radius are particularly common, what is needed is an external fixation device configured particularly for the treatment of such fractures, without the bulk, weight, and complexity of a general purpose device.